Because of the widespread popularity of computers, most people have become comfortable with conventional computer input devices such as keyboards and pointing devices. The keystrokes and movements of mice, trackballs, and joysticks are sufficiently intuitive to provide satisfactory interfaces for most computer-related tasks. Nonetheless, as computers become increasingly more indispensable, limits of a human-machine interface that depends upon pressing buttons and dragging a pointer with a mouse or other device tends to restrict how quickly and naturally computers can be used.
In seeking to further enhance the human-machine interface, ever-improving hardware capabilities have made possible systems that avoid the need to enter text with a keyboard. Personal digital assistants and tablet PCs can now recognize human handwriting. Speech recognition software enables users to operate computers and enter text by speaking into a microphone. Such systems can thus provide a more efficient and satisfying experience for users who prefer not to type on a keyboard or are less proficient in doing so.
As computers become more ubiquitous throughout our environment, the desire to make computers and their interfaces even more user-friendly continues to promote development in this area. For example, the MIT Media Lab, as reported by Brygg Ullmer and Hiroshi Ishii in “The metaDESK: Models and Prototypes for Tangible User Interfaces,” Proceedings of UIST10/1997:14-17,” has developed another form of “keyboardless” human-machine interface. The metaDESK includes a generally planar graphical surface that not only displays computing system text and graphic output, but also receives user input by responding to an object placed against the graphical surface. The combined object responsive and display capability of the graphical surface of the metaDESK is facilitated using infrared (IR) lamps, an IR camera, a video camera, a video projector, and mirrors disposed beneath the surface of the metaDESK. The mirrors reflect the graphical image projected by the projector onto the underside of the graphical display surface to provide images that are visible to a user from above the graphical display surface. The IR camera can detect IR reflections from the undersurface of an object placed on the graphical surface.
Others have been developing similar keyboardless interfaces. For example, papers published by Jun Rekimoto of the Sony Computer Science Laboratory, Inc. and associates describe a “HoloWall” and a “HoloTable” that display images on a surface and use IR light to detect objects positioned adjacent to the surface.
By detecting a specially formed object or by detecting IR-reflected light from an object disposed on a graphical display surface, the metaDESK can respond to the contemporaneous placement and movement of the object on the display surface to carry out a predefined function, such as displaying and moving a map of the MIT campus.
Thus, computing systems such as the HoloWall and metaDESK may provide a more natural degree of human-machine interaction by providing the means for a computer to respond to specific objects. However, while such systems enable a person to interact with a computer by engaging and moving a physical object instead of a keyboard or mouse, the quality of the experience can be undermined somewhat if the object bears a bar code or other visible code detectable by the detectors used in those systems that is also readily apparent to the user. Further, in the case of a game where it is desirable to keep secret a value or identity of a game piece or playing card, a visible code might give away the value or identity to a savvy, observant competitor.
In the latter case, the presence of a visible IR code may be masked with a filter that is transparent to IR light but opaque to visible light. With such a filter, the IR detectors might still detect the code on the physical object, but the users would not be able to see it. Thus, hiding the codes with filters can restore some of the mystique of the computing system that appears to recognize each object that is placed on an interactive surface, without any apparent way being provided to enable such recognition.
Unfortunately, the use of filters does not necessarily lend itself to every desired application. Attaching thick filters to surfaces of objects may be just as apparent, if not more conspicuous, than allowing the codes to remain visible. Further, attaching filters to thin objects may not be practical. For example, if a number of cards are to be encoded for use with such a system, applying filters might make the cards too large or clumsy to handle, to be convenient. Ultimately, it would be desirable to be able to encode objects discreetly, without making the markings visible or using conspicuous filters.